A conventional combustible gas turbine engine includes a compressor, a combustor, and a turbine. The engine further comprises an outer casing which defines an outer section for each of the compressor, combustor and turbine. The compressor compresses ambient air. The combustor combines the compressed air with a fuel and ignites the mixture creating combustion products defining a working gas. The working gas travels to the turbine. Within the turbine section of the outer casing are a series of rows of stationary vanes and rotating blades. Each pair of rows of vanes and blades is called a stage. Typically, there are four stages in a turbine. The rotating blades are coupled to a shaft and disc assembly. As the working gas expands through the turbine, the working gas causes the blades, and therefore the shaft and disc assembly, to rotate.
Typically, turbine blades comprise a root, a platform and an airfoil that extends outwardly from the platform. The airfoil is ordinarily composed of an outer end or tip, a leading edge, a trailing edge, a concave pressure side and a convex suction side. Side walls are integrally formed together to define the pressure and suction sides and the leading and trailing edges of the airfoil. The tip may be defined by a squealer portion and a cap. Outer ends of the side walls form a raised lip extending around an outer periphery of the airfoil. The raised lip defines the airfoil squealer portion. Notches are formed in the side walls just below the squealer portion. The cap is defined by one or more plates received in the notches. Brazing material is employed to hold the plates in the notches.
During operation of the gas turbine engine, the airfoil tips wear due to engagement with the outer casing. Also one or more cracks may develop near an airfoil tip due to fatigue stresses imparted on the tip during the operation of the turbine engine. Airfoil tip wear may be repaired by machining off the squealer portion, the cap and any braze material provided to secure the cap plate(s) to the airfoil side walls. If a crack is present, the material adjacent the crack is also removed so as to form a crack repair volume, which is filled by welding, see U.S. Pat. No. 6,332,272 B1 (hereinafter the '272 patent), the entire disclosure of which is incorporated herein by reference. A replacement cap is welded to the machined outer ends of the airfoil side walls, see the '272 patent. A replacement squealer portion may then be welded to the replacement cap and the outer ends of the airfoil side walls, see the '272 patent.
It is known to use liquid-cooled metal chill blocks to cool an airfoil during airfoil tip welding repair operations. By cooling the airfoil during one or more welding repair operations, the chills blocks reduce the possibility that a thermally induce crack may form in the blade during the repair operation. The chill blocks are traditionally formed from cast aluminum or copper metal blocks. The cast metal blocks are machined to match the contour of the blade surfaces. Casting and machining metal blocks to form a chill block for each blade design is costly and, hence, disadvantageous.
Accordingly, there is a need for an improved process and apparatus for cooling an airfoil of a blade during a welding repair operation.